5 The lengths, \(t\) minutes, of 242 phone calls made by a family over a period of 1 week are summarised in the frequency table below.
| Length of phone | | call \(( t\) minutes \()\) |
| \(0 < t \leqslant 1\) | \(1 < t \leqslant 2\) | \(2 < t \leqslant 5\) | \(5 < t \leqslant 10\) | \(10 < t \leqslant 30\) |
| Frequency | 14 | 46 | 102 | \(a\) | 40 |
- Find the value of \(a\).
- Calculate an estimate of the mean length of these phone calls.
- On the grid, draw a histogram to illustrate the data in the table.
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